linux-kernel - [PATCH 4.16 090/196] ext4: fix offset overflow on 32-bit archs in ext4_iomap

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Date:   Sun, 22 Apr 2018 15:51:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>,
        Jan Kara <jack@...e.cz>, Theodore Tso <tytso@....edu>
Subject: [PATCH 4.16 090/196] ext4: fix offset overflow on 32-bit archs in ext4_iomap_begin()

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Slaby <jslaby@...e.cz>

commit fe23cb65c2c394ea306f3714a17d46ab2e6a0af1 upstream.

ext4_iomap_begin() has a bug where offset returned in the iomap
structure will be truncated to unsigned long size. On 64-bit
architectures this is fine but on 32-bit architectures obviously not.
Not many places actually use the offset stored in the iomap structure
but one of visible failures is in SEEK_HOLE / SEEK_DATA implementation.
If we create a file like:

dd if=/dev/urandom of=file bs=1k seek=8m count=1

then

lseek64("file", 0x100000000ULL, SEEK_DATA)

wrongly returns 0x100000000 on unfixed kernel while it should return
0x200000000. Avoid the overflow by proper type cast.

Fixes: 545052e9e35a ("ext4: Switch to iomap for SEEK_HOLE / SEEK_DATA")
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Signed-off-by: Jan Kara <jack@...e.cz>
Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...r.kernel.org # v4.15
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/ext4/inode.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3524,7 +3524,7 @@ retry:
 		iomap->flags |= IOMAP_F_DIRTY;
 	iomap->bdev = inode->i_sb->s_bdev;
 	iomap->dax_dev = sbi->s_daxdev;
-	iomap->offset = first_block << blkbits;
+	iomap->offset = (u64)first_block << blkbits;
 	iomap->length = (u64)map.m_len << blkbits;
 
 	if (ret == 0) {